80 lines
2.5 KiB
Markdown
80 lines
2.5 KiB
Markdown
|
---
|
|||
|
|
id: 587d7fb1367417b2b2512bf4
|
|||
|
|
title: 通過鏈式調用中間件來創建時間服務
|
|||
|
|
challengeType: 2
|
|||
|
|
forumTopicId: 301510
|
|||
|
|
dashedName: chain-middleware-to-create-a-time-server
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
# --description--
|
|||
|
|
|
|||
|
|
使用 `app.METHOD(path, middlewareFunction)` 可以在指定的路由掛載中間件， 也可以在路由定義中鏈式調用中間件。
|
|||
|
|
|
|||
|
|
請看以下示例：
|
|||
|
|
|
|||
|
|
```js
|
|||
|
|
app.get('/user', function(req, res, next) {
|
|||
|
|
req.user = getTheUserSync(); // Hypothetical synchronous operation
|
|||
|
|
next();
|
|||
|
|
}, function(req, res) {
|
|||
|
|
res.send(req.user);
|
|||
|
|
});
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
此方法可用於將服務操作拆分爲較小的單元， 這可以讓應用擁有更好的結構，也便於在不同的位置上覆用代碼； 此方法還可用於對數據執行某些驗證。 可以在每一箇中間件堆棧中，阻止當前鏈的執行，並將控制權傳遞給專門設計用於處理錯誤的函數； 或者可以將控制權傳遞給下一個匹配的路由，以處理特殊情況， 我們將在高級 Express 章節中看到這些內容。
|
|||
|
|
|
|||
|
|
# --instructions--
|
|||
|
|
|
|||
|
|
在路由 `app.get('/now', ...)` 中鏈式調用中間件函數，並在最後處理。 在中間件函數中給請求對象中的 `req.time` 添加到當前時間， 可以使用 `new Date().toString()`， 在處理函數中，使用 `{time: req.time}` 結構的 JSON 對象來響應請求。
|
|||
|
|
|
|||
|
|
**注意：** 如果不鏈式調用中間件，測試將不能通過。 如果將中間件函數掛載在其他地方，即使輸出結果正確，測試也會失敗。
|
|||
|
|
|
|||
|
|
# --hints--
|
|||
|
|
|
|||
|
|
/now 接口應該已經掛載了中間件
|
|||
|
|
|
|||
|
|
```js
|
|||
|
|
(getUserInput) =>
|
|||
|
|
$.get(getUserInput('url') + '/_api/chain-middleware-time').then(
|
|||
|
|
(data) => {
|
|||
|
|
assert.equal(
|
|||
|
|
data.stackLength,
|
|||
|
|
2,
|
|||
|
|
'"/now" route has no mounted middleware'
|
|||
|
|
);
|
|||
|
|
},
|
|||
|
|
(xhr) => {
|
|||
|
|
throw new Error(xhr.responseText);
|
|||
|
|
}
|
|||
|
|
);
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
/now 接口應該返回一個現在時間 +/-20 秒的時間
|
|||
|
|
|
|||
|
|
```js
|
|||
|
|
(getUserInput) =>
|
|||
|
|
$.get(getUserInput('url') + '/_api/chain-middleware-time').then(
|
|||
|
|
(data) => {
|
|||
|
|
var now = new Date();
|
|||
|
|
assert.isAtMost(
|
|||
|
|
Math.abs(new Date(data.time) - now),
|
|||
|
|
20000,
|
|||
|
|
'the returned time is not between +- 20 secs from now'
|
|||
|
|
);
|
|||
|
|
},
|
|||
|
|
(xhr) => {
|
|||
|
|
throw new Error(xhr.responseText);
|
|||
|
|
}
|
|||
|
|
);
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
# --solutions--
|
|||
|
|
|
|||
|
|
```js
|
|||
|
|
/**
|
|||
|
|
Backend challenges don't need solutions,
|
|||
|
|
because they would need to be tested against a full working project.
|
|||
|
|
Please check our contributing guidelines to learn more.
|
|||
|
|
*/
|
|||
|
|
```
|